[PATCH] malloc: Improve thp_init

[Adhemerval Zanella Netto]

On 12/12/25 15:29, Wilco Dijkstra wrote:
> 
> Cleanup thp_init, change it so that the DEFAULT_THP_PAGESIZE
> setting can be overridden with glibc.malloc.hugetlb=0 tunable.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> 
> ---
> 
> diff --git a/malloc/malloc.c b/malloc/malloc.c
> index 08ca1879ac7bfab2de7310f094ec7fe639c96f99..be29929993a2f7f3d269e7d9ed9952cf0d8f109d 100644
> --- a/malloc/malloc.c
> +++ b/malloc/malloc.c
> @@ -1902,25 +1902,29 @@ free_perturb (char *p, size_t n)
>  
>  /* ----------- Routines dealing with transparent huge pages ----------- */
>  
> -static void thp_init (void);
> +static __always_inline void
> +thp_init (void)
> +{
> +  /* Initialize only once if DEFAULT_THP_PAGESIZE is defined.  */
> +  if (!DEFAULT_THP_PAGESIZE || mp_.thp_mode != malloc_thp_mode_not_supported)
> +    return;
> +
> +  /* Set thp_pagesize even if thp_mode is never.  This reduces frequency
> +     of MORECORE () invocation.  */
> +  mp_.thp_mode = __malloc_thp_mode ();
> +  mp_.thp_pagesize = DEFAULT_THP_PAGESIZE;
> +}
>  
>  static inline void
>  madvise_thp (void *p, INTERNAL_SIZE_T size)
>  {
>  #ifdef MADV_HUGEPAGE
>  
> -  /* Ensure thp_init () is invoked only once */
> -  if (mp_.thp_pagesize < DEFAULT_THP_PAGESIZE)
> -    thp_init ();
> +  thp_init ();
>  
> -  /* Only use __madvise if the system is using 'madvise' mode.
> -     Otherwise the call is wasteful. */
> -  if (mp_.thp_mode != malloc_thp_mode_madvise)
> -    return;
> -
> -  /* Do not consider areas smaller than a huge page or if the tunable is
> -     not active.  */
> -  if (mp_.thp_pagesize == 0 || size < mp_.thp_pagesize)
> +  /* Only use __madvise if the system is using 'madvise' mode and the size
> +     is at least a huge page, otherwise the call is wasteful. */
> +  if (mp_.thp_mode != malloc_thp_mode_madvise || size < mp_.thp_pagesize)
>      return;
>  
>    /* Linux requires the input address to be page-aligned, and unaligned
> @@ -2468,9 +2472,8 @@ sysmalloc (INTERNAL_SIZE_T nb, mstate av)
>           previous calls. Otherwise, we correct to page-align below.
>         */
>  
> -      /* Ensure thp_init () is invoked only once */
> -      if (mp_.thp_pagesize < DEFAULT_THP_PAGESIZE)
> -        thp_init ();
> +      /* Ensure thp_pagesize is initialized.  */
> +      thp_init ();
>  
>        if (__glibc_unlikely (mp_.thp_pagesize != 0))
>  	{
> @@ -5126,7 +5129,9 @@ do_set_mxfast (size_t value)
>  static __always_inline int
>  do_set_hugetlb (size_t value)
>  {
> -  if (value == 1)
> +  if (value == 0)
> +    mp_.thp_mode = malloc_thp_mode_never;
> +  else if (value == 1)
>      {
>        mp_.thp_mode = __malloc_thp_mode ();
>        if (mp_.thp_mode == malloc_thp_mode_madvise
> @@ -5139,15 +5144,6 @@ do_set_hugetlb (size_t value)
>    return 0;
>  }
>  
> -static __always_inline void
> -thp_init (void)
> -{
> -  /* thp_pagesize is set even if thp_mode is never. This reduces frequency
> -     of MORECORE () invocation.  */
> -  mp_.thp_pagesize = DEFAULT_THP_PAGESIZE;
> -  mp_.thp_mode = __malloc_thp_mode ();
> -}
> -
>  int
>  __libc_mallopt (int param_number, int value)
>  {
> diff --git a/sysdeps/unix/sysv/linux/aarch64/malloc-hugepages.h b/sysdeps/unix/sysv/linux/aarch64/malloc-hugepages.h
> index f432ff7f0ce0f56f6a761aeff293fe2f5d5d2542..662f75cb78491da014f2b91b848c8b7b162742a4 100644
> --- a/sysdeps/unix/sysv/linux/aarch64/malloc-hugepages.h
> +++ b/sysdeps/unix/sysv/linux/aarch64/malloc-hugepages.h
> @@ -16,6 +16,6 @@
>     License along with the GNU C Library; see the file COPYING.LIB.  If
>     not, see <https://www.gnu.org/licenses/>.  */
>  
> -# define DEFAULT_THP_PAGESIZE	1UL << 21
> +#define DEFAULT_THP_PAGESIZE	(1UL << 21)
>  
>  #include_next <malloc-hugepages.h>
> 
>